The present invention relates to processes and apparatus for treating electronic components and, in particular, to processes and apparatus for treating semiconductor wafers with a combination of a heated solvent and an ozonated process fluid to remove or strip bulk photoresist.
Wet processing of electronic components, such as semiconductor wafers, flat panels, and other electronic component precursors is used extensively during the manufacture of integrated circuits. Semiconductor fabrication is described generally, for example, in P. Gise et al., Semiconductor and Integrated Circuit Fabrication Techniques (Reston Publishing Co. Reston, Va. 1979), the disclosure of which is herein incorporated by reference in its entirety.
Preferably, wet processing is carried out to prepare the electronic components for processing steps such as diffusion, ion implantation, epitaxial growth, chemical vapor deposition, hemispherical silicon grain growth, or combinations thereof. During wet processing, the electronic components are contacted with a series of processing solutions. The processing solutions may be used, for example, to etch, remove photoresist, clean, grow an oxide layer, or rinse the electronic components. See, e.g., U.S. Pat. Nos. 4,577,650; 4,740,249; 4,738,272; 4,856,544; 4,633,893; 4,778,532; 4,917,123; and EP 0 233 184, assigned to a common assignee, and Burkman et al., Wet Chemical Processes-Aqueous Cleaning Processes, pg. 111-151 in Handbook of Semiconductor Wafer Cleaning Technology (edited by Werner Kern, Published by Noyes Publication Parkridge, New Jersey 1993), the disclosures of which are herein incorporated by reference in their entirety.
There are various types of systems available for wet processing. For example, the electronic components may be processed in a single vessel system closed to the environment (such as an Omni system employing Full-Flow(trademark) technology supplied by Mattson Technology, Inc.), a single vessel system open to the environment, or a muliple open bath system (e.g., wet bench) having a plurality of baths open to the atmosphere.
Following processing, the electronic components are typically dried. Drying of the semiconductor substrates can be done using various methods, with the goal being to ensure that there is no contamination created during the drying process. Methods of drying include evaporation, centrifugal force in a spin-rinser-dryer, steam or chemical drying of wafers, including the methods and apparatus disclosed in, for example, U.S. Pat. No. 4,911,761.
An important consideration for an effective wet processing method is that the electronic component produced by the process be ultraclean (i.e., with minimum particle contamination and minimum chemical residue). An ultraclean electronic component is preferably free of particles, metallic contaminants, organic contaminants, and native oxides; has a smooth surface; and has a hydrogen-terminated surface. Although wet processing methods have been developed to provide relatively clean electronic components, there is always a need for improvement because of the intricacies associated with technological advances in the semiconductor industry. One of the most challenging problems of attaining ultraclean products is the removal of photoresist.
The use of ozone for removing organic material, such as photoresist, from semiconductor wafers has been investigated. For example, U.S. Pat. No. 5,464,480 issued to Matthews (hereinafter xe2x80x9cMatthewsxe2x80x9d), describes a process in which semiconductor wafers are contacted with a solution of ozone and water at a temperature of about 1xc2x0 C. to about 15xc2x0 C. Matthews discloses, for example, placing the semiconductor wafers into a tank containing deionized water, diffusing ozone into the deionized water for a time sufficient to oxidize the organic materials from the wafers, while maintaining the temperature of the water at between about 1xc2x0 C. to about 15xc2x0 C., and then rinsing the wafers with deionized (DI) water. Matthews further discloses exposing the wafers to ultraviolet light during the process.
Various other methods have been investigated using ozone in conjunction with water to strip organic materials from the surface of semiconductor wafers or to rinse wafers after chemical processing. For example, in one such method, ozone gas is generated in an ozone generator and fed to an ozonator where the ozone gas is mixed with DI water. The ozone gas is also simultaneously fed to the bottom of the process vessel via a specially designed device that provides a uniform stream of gaseous ozone into the bath. Matthews et al., Mat. Res. Soc. Symp. Proc., 1997, 477, 173-78. See also 1997 Joint Int""l Mtg. of Electro. Chem. Soc""y and Int""l Soc""y. of Electro., Abstract 1886, p. 2169 submitted by Kenens et al.; Id. at Abstract 1887, p. 2170, submitted by Wolke et al.; Id. at Abstract 1892, p. 2176, submitted by Fukazawa et al.; Id. at Abstract 1934, p. 2236, submitted by Kashkoush et al.; Id. at Abstract 1890, p. 2173, submitted by Li et al.; Id. at Abstract 1891, p. 2174, submitted by Joo et al.; Ultra Clean Processing of Silicon Surfaces UCPSS 1996, Kenens et al., Removal of Organic Contamination From Silicon Surfaces, p. 107-110.
In another method, the use of ozone-injected ultrapure water (ozone concentration of about 1-2 ppm) is applied to the RCA or other similar cleaning methods. The ozonated water is used to remove organic impurities. The wafers are then treated with NH4OH and H2O2 to remove metallic ion contaminants, followed by a treatment with HF and H2O2 to remove native oxide and metal, and to improve surface smoothness. The wafers are then rinsed with DI water. The ozone gas is generated by electrolyzing ultra pure water. The generated ozone gas is then dissolved in ultrapure water through a membrane. Ohmi et al., J. Electrochem. Soc""y 140, 1993, 804-10.
Another method uses a moist ozone gas phase. In this method, a quartz container is filled with a small amount of liquid, sufficient to immerse an O3 diffuser. The liquid is DI water spiked with additives such as hydrogen peroxide or acetic acid, if appropriate. A lid is placed on the container and the liquid is heated to 80xc2x0 C. Wafers are placed directly above the liquid interface (i.e., the wafers are not immersed in the liquid). Heating of the liquid in a sealed container and continuous O3 bubbling through the liquid exposes the wafers to a moist ambient O3 environment. De Gendt et al., Symp. VLSI Tech. Dig. Tech. Papers, 1998, 168-69. The De Gendt paper further describes a method whereby a quartz tank is filled with 7 liters of liquid, an ozone diffuser is located at the bottom of the tank, and the liquid is heated. The wafers are positioned directly above the ozone diffuser and immersed in the liquid such that O2/O3 bubbles contact the wafer surfaces. The De Gendt paper also reports that OH radical scavengers such as acetic acid can enhance process efficiency.
In another method, photoresist removal is carried out in a gas phase reactor at a temperature of between about 200-300xc2x0 C. In certain instances, additives such as N2O gas are mixed with the ozone gas. See Olness et al., Mat. Res. Soc""y. Symp., 135, 1993, 261-66.
Spin cleaning techniques using ozonated water have also been investigated. See, e.g., Cleaning Technology In Semiconductor Device Manufacturing Symposium, Yonekawa et al., Contamination Removal By Wafer Spin Cleaning Process With Advanced Chemical Distribution System, 94-7, 94-101; 1997 Joint Int""s Mtg. of Electro. Chem. Soc""y and Int""l Soc""y. of Elctro., Abstract 1888, p. 2171 submitted by Osaka et al.
The use of ozone with cleaning solutions has also been investigated. One such method uses a wafer cleaning sequence with a single-wafer spin using ozonated water and dilute HF to remove contaminants such as particles, metallics, and organics from the wafer surfaces. The method consists of pouring ozonated water on a wafer surface for 10 seconds, followed by pouring dilute HF over the wafers for 15 seconds. This cycle is repeated until the desired results are achieved. 1997 Joint Int""s Mtg. of Electro. Chem. Soc""y and Int""l Soc""y. of Elctro., Abstract 1888, p. 2171 submitted by Tsutomu et al.; see also Id. at Abstract 1889, p. 2172, submitted by Han et al.; Id. at Abstract 1892, p. 2176, submitted by Fukazawa et al.; Ultra Clean Processing of Silicon Surfaces UCPSS 1996, Kenens et al., Removal of Organic Contamination From Silicon Surfaces, p. 107-10.
Cleaning of semiconductor wafers has also been carried out using gaseous ozone and other chemicals such as hydrofluoric acid and hydrochloric acid to remove residual contaminating particles. For example, U.S. Pat. No. 5,181,985 to Lampert et. al., (hereafter, xe2x80x9cLampertxe2x80x9d) discloses a cleaning process where water is sprayed at a temperature of 10xe2x96xa1 C. to 90xc2x0xe2x96xa1 C. onto semiconductor wafers and a chemically active gaseous substance such as ammonia, hydrogen chloride, ozone, ozonized oxygen, chlorine, or bromine is introduced. In Lampert, ozone or ozonized oxygen is used to form a superficial oxide which is then subsequently removed with hydrofluoric acid or hydrochloric acid.
Ozone has also been used in conjunction with sulfuric acid as a means for stripping photoresist from semiconductor wafers. See, e.g., U.S. Pat. Nos. 4,899,767 and 4,917,123 issued to CFM Technologies. The methods described in the CFM patents are carried out in a single vessel system and, generally, a solution of sulfuric acid is spiked with an oxidizing agent such as ozone. Other systems using sulfuric acid in conjunction with ozone may employ a gas distribution system that includes a sparger plate with holes for distributing gas through a bath in the tank. See, e.g., U.S. Pat. No. 5,082,518 assigned to SubMicron. SubMicron""s patent describes the use of an apparatus that distributes ozone directly into the treatment tank containing the sulfuric acid.
Ozone ashing has also been investigated as a means for removing photoresist material from wafers. In this method, photoresist is oxidized at higher temperatures (250-350xc2x0 C.) by two strong oxidizing gases, ozone and atomic oxygen. A small amount of excited nitrous oxide enhances the ashing rate. See Olness et al., Mat. Res. Soc""y. Symp., 135, 1993, 261-66.
U.S. Pat. No. 5,503,708 to Koizumi et al., (xe2x80x9cKoizumixe2x80x9d) discloses an alternative apparatus and method using gaseous ozone for removing a photoresist film from a semiconductor wafer. In Koizumi, an apparatus is used that processes a single wafer at a time. The apparatus exposes the wafer to a gas mixture containing ozone and alcohol while the wafer surface is preferably heated to a temperature of 150xc2x0 C. to 250xc2x0 C. to effect removal of the photoresist.
The use of ozone in precleaning steps has also been explored. In one such method, as disclosed in U.S. Pat. No. 5,762,755 to McNeilly et al., a wafer contaminated with organics is held in a partial vacuum and heated to at least 200xc2x0 C. by radiation and then exposed to ozone. The wafer is then cooled to, or below, 80xc2x0 C. and then exposed to ultraviolet excited chlorine.
Another method for pre-cleaning wafers uses an O3/IR process as an in situ cleaning step for organic removal before oxide etching to condition the surface and to assure etch repeatability and uniformity. As a posttreatment step, a thin layer of oxide may be grown on the wafer surface. In this process, the ozone is fed into the process chamber while the wafer is being heated by an infrared lamp to a certain temperature, after which the ozone is turned off and the wafer is cooled down by a low temperature inert gas. Cleaning Technology In Semiconductor Device Manufacturing Symposium, Kao et al., Vapor-Phase pre-Cleans for Furnace-Grown and Rapid-Thermal Thin Oxides, 1992, 251-59.
The use of ozone gas in conjunction with ultraviolet light for cleaning and etching wafer surfaces has also been investigated. See Semiconductor Wafer Cleaning and Surface Characterization (proceedings of the 2nd workshop), Moon, Si Wafer Cleaning Study by UV/Ozone ands In Situ Surface Analysis, 68-76; ASM Int""l, Li et al., UV/Ozone Pre-Treatment on Organic Contaminated Wafer for Complete Oxide Removal in HF Vapor Cleaning. 
It is known to remove photoresist from electronic components using ashing processes. However, complete removal of the photoresist with ashing is difficult to achieve because the ashing process itself can harm the electronic components surface. For example, ashing with CF4 on bare silicon surfaces induces pits and, accordingly, a full ash down should typically be avoided. Further, low temperature ashing is often necessary to avoid resist popping. Consequently, the use of ashing processes typically requires one or more post-ashing processing steps (e.g., clearing and/or cleaning the component with processing solutions such as a SOM or HPM solution) to completely remove the photoresist.
There have been several attempts over the last years to use ozone (O3 ) for bulk photoresist stripping. However, the use of ozonated process fluids (e.g., ozonated deionized water) has traditionally suffered from unsatisfactorily low etch rates.
Other process solutions (xe2x80x9cdesignerxe2x80x9d solvents and/or isopropyl alcohol) have been employed for the removal of photoresist. However, the use of such process solutions can be prohibitively expensive, may require long bath lifetimes, and may involve serious environmental risk (i.e., pollution and safety).
The present invention provides commercially viable (i.e., cost efficient and rapid) apparatus and processes for treating electronic components, such as semiconductor wafers. In one of its aspects, the present invention relates to a process for treating an electronic component wherein the electronic is first exposed to a heated solvent and subsequently exposed to an ozonated process fluid. In one embodiment, the heated solvent comprises boiling isopropyl alcohol (IPA) and the ozonated process fluid comprises ozonated deionized water. The heated solvent is preferably formed as a heated solvent layer prior to exposing the heated solvent to the electronic component.
In another of its aspects, the present invention relates to an apparatus for treating an electronic component having a chamber for holding the electronic component. The chamber preferably comprises a closed, direct displacement chamber system. The apparatus also includes a heated solvent source for supplying a heated solvent to the chamber and an ozonated process fluid source for supplying an ozonated process fluid to the chamber. In one embodiment, the heated solvent source supplies a layer of heated solvent to the chamber.
Additional features and embodiments of the present invention will become apparent to those skilled in the art in view of the ensuing disclosure and appended claims.